When the mayor stands up to deliver his State of the City speech today, many will be watching to see how he responds to the political threat that is waxing on his right flank. We speak of the prospect that he is going to be challenged in the Republican mayoral primary in September 2005. Certainly he is aware of the danger, as it is what has so irked him about the plan being hatched in the City Council to expand public financing of local political campaigns. Our Jack Newfield marked this point last month. It’s no doubt too soon to start making book on the primary. But the logic is not lost on Councilman Tom Ognibene, who is now stating that a year and a half from now he is going to challenge the mayor for the Republican nomination.

A brief talking-points memo that reached our desk starts with the fact that there are but a few more than 500,000 registered Republicans, of whom only 20% or so would normally vote in a primary. In a contested primary, these talking points note, that number might go as high as 30% or 35%. It would take, in any event, only 80,000 or 100,000 votes to win the GOP mayoral primary, and those are the kinds of numbers that can be affected by several million dollars in campaign cash. So if the City Council amends the law and moves the ratio of matching funds to 8-to-1 from its current level of 4-to-1, the impact could be enormous.

If Mr. Ognibene — or another challenger — could raise $250 from 1,000 people, say, his quarter of a million dollar war chest would suddenly balloon by another $2 million. “Given the ‘free media’ he’d get, plus the couple of million he’d have to play with, he’d have a shot,” is the way it is put in the memo wired to us. This is underscored by the defeat that was dealt to the mayor on the issue of nonpartisan elections, where the mayor was humiliated at the polls though he spent about $7.5 million and opponents spent but a tenth that amount. A serious candidate, the memo says, would force the mayor to spend time on a primary that he’d rather spend on the general election.

When we phoned Mr. Ognibene to ask about this, he was straightforward. He said he’s going to run because he has felt “deeply betrayed” by the way the mayor has moved away from the Republican agenda. He acknowledges the mayor’s recent talk about scaling back his tax increase, which, our Dina Temple-Raston reports on Page One, will be made formal by the mayor today. Mr. Ognibene suggests the mayor is “trying to win back the Republican Party.” But Mr. Ognibene is not buying it for a moment. “Fool me once, shame on you,” he says. “Fool me twice, shame on me.” He derides the notion that the mayor would be supportive of the Republican agenda in a second and last term.”Let the people who are going to vote in the Republican primary answer that,” Mr. Ognibene says.

Like we do, Mr. Ognibene has a reserve about the whole idea of forcing taxpayers to pay for political campaigns. But campaign finance regulation starts to have its own unintended consequences. Mr. Ognibene is an ordinary attorney from Middle Village, Queens. He eschewed lucrative private practice and spent more than a decade in public service. Under the current law, individuals like him would be forbidden to accept contributions above $4,950 unless they reject public financing. Certain limits also obtain, even if such individuals eschew public financing and even if they’re running against a billionaire prepared to campaign with tens of millions of dollars of his own money, as Mr. Bloomberg did the last time out. In any event, Mr. Ognibene says, the expansion in matching funds is something he expects the speaker of the City Council, Gifford Miller, is going to pursue vigorously.

Even were Mr. Bloomberg denied the Republican nomination, it wouldn’t automatically mean that he would be driven from City Hall. One scenario would have Mr. Bloomberg stand on the line of the Independence Party and try to snatch a victory, much the way the Republican patrician Mayor Lindsay did as a candidate of the Liberal Party when, in 1969, the Staten Island Republican John Marchi denied him the Republican nomination for a second term. Were that to happen, however, Mr. Bloomberg would have to answer those wondering what he would owe to the Independence Party’s demagogic Lenora Fulani.

A lot can happen between now and September 2005. The Republican congressman from Staten Island, Vito Fossella, is being awfully coy about his own plans, as our Alicia Colon discovered when she dropped by to see him last month.”The mayor,” Mr. Ognibene notes, “is deathly afraid of Vito Fossella.” It could be that the real Republicans will get cold feet at the prospect that purging the mayor from the Republican line might give the mayoralty to a Democrat. But the Democrats themselves could fracture, if, say, one of their disaffected stars were to seek the mayoralty on a minor party line, such as Working Families. So it’s not too soon to note that Mr. Bloomberg will have to look sharp if he is to avoid being outmaneuvered on the right flank that he has seemed so far to take entirely for granted.